Lightweight grades of paper which have a soft absorbing texture are formed by drying the paper web on a single large drying cylinder referred to as a Yankee dryer. The lightweight paper web, after being formed in the forming section of a papermaking machine and pressed in a press section, is dried on the surface of the Yankee dryer. The paper web is pressed on the Yankee dryer by a press roll. The Yankee dryer is heated by steam which is supplied to the interior of the Yankee dryer. An aircap placed over the top of the Yankee dryer blows high velocity heated air down onto the dryer surface to increase the drying rate of the Yankee dryer.
The paper dried on the Yankee dryer is given its characteristic absorbency by a creping action which takes place at the doctor blade which scrapes off paper from the surface of the Yankee dryer. The scraping action of the doctor blade compresses the paper about 3 to 75 percent. Lightweight grades of tissue which are produced on the Yankee dryer are fabricated at relatively high-speed. The highest speed Yankee dryers currently operate at about 6,700 feet per minute before the paper is compressed in the creping process.
The high speed at which tissue types of paper are manufactured combined with the creping action which removes the paper from the surface of the Yankee dryer produces large quantities of paper fiber dust. The dust is a fire hazard, increases maintenance costs and can contaminate the product. The dust also creates health concerns. The low strength of the tissue as it is removed from the Yankee dryer by the doctor blade and an unstable web run can create problems and lead to frequent breaks of the paper web. Increasing web tension to avoid paper breaks by increasing tension produced by the reel can result in the web being stretched which reduces its absorbency.
In existing tissue making machines the necessity of frequently cleaning and removing broke from the vicinity of the doctor blade has prevented the placement of any support sufficiently close to the doctor blade to prevent occasional paper breaks.
Skinning doctor blades positioned in front of the creping doctor have been used to deflect air from the aircap and from the air naturally moving with the paper web away from the web before it is scraped from the Yankee dryer roll, yet the effectiveness of such skinning doctor blades is limited.
What is needed is a tissue web support device which can decrease paper breaks and the amount of dust generated as a tissue web is scraped off the surface of the Yankee dryer.